Electro-acoustical delay line useful for producing reverberation in electrical musical instruments



I. DANIEL 3,092,792

INE USEFUL FOR PRODUCING ELECTRO-ACOUSTICAL DELAY L REVERBERATION INELECTRICAL MUSICAL INSTRUMENTS Filed July 3, 1961 INVENTOR. M d 47/a BYATTORNEY United States Patent Oil ice This invention relates toelectrical musical instruments and more particularly to an apparatus forproducing mechanical reverberation in the transmission of sound signals.The apparatus is, in general, of the type disclosed in Hammond PatentNo. 2,230,836, dated February 4,

1941. It was pointed out in the above patent that the apparatus theredisclosed was capable of producing tones having reverberation eifectswhich simulated the reverberation characteristics of a large auditoriumeven though the apparatus was being used in a small non-reverberative'room or out-of-doors. This invention also has that objective but it is aconsiderable improvement in that the character of the reverberation iscontrolled substantially completely by the tone signals and is notaffected by other considerations such as physical vibrations of theapparatus whether originating externally of the unit or produced throughsound waves emanating from the speaker.

I have produced a simplified reverberation unit wherein an electricaltransducer, such as a piezoelectric crystal functions as a sendingelement in applying sound vibrations through a coil spring system, thelower end of which system is in turn connected to a piezoelectricreceiving transducer which essentially reproduces the sound signals butwith a delay caused by the travel of the vibrations along the springsystem. Broadly this initself is old. However, the piezoelectriccrystals must be anchored at one end thereof so that the stimulation ofthe other end mal be translated into physical movement, in the case ofthe sending transducer, and electrical signals in the case of thereceiving transducer.

However, such anchoring has itself caused difficulties in that externalphysical vibrations would often be introduced into the system so as toproduce spurious and undesired reverberative effects. For example,assume that the receiving crystal is physically actuated by the springto producerever berative signals. Assumealso that an outside eiiect suchas persons dancing in the room would agitate the crystal and producereverberation effects which were completely unrelated to the soundsignals through the apparatus. This results in spurious reverberationeffects and, indeed, can even cancel the properly transmitted signals.

With the above in mind, I have provided a reverbera tion system whereinthe transducer crystals are anchored only so far as they must respond tothe stimulation of the sound signals through the apparatus. They are,however, tree to move in both horizontal and vertical planes in such amanner that they are substantially isolated from external noises andwill respond substantially solely to the desired signals. This lastdescription assumes the use of a piezoelectric crystal which respondswith or reacts to twisting or torsional effects.

The invention will be further understood from the following descriptionand drawings in which:

FIGURE 1 is a longitudinal cross-sectional view of a reverberation unitconstructed according to the instant invention;

FIGURE 2 is an elevational view thereof, partly broken away; and

FIGURE 3 is an enlarged fragmentary view illustrating the connection ofthe spring system to the end walls.

It will be understood that the reverberation unit herein disclosedtranslates audio waves or signals into mechanical vibrations, effects adelay in the vibrations, and then translates the vibrations back intoelectrical audio waves or signals. Accordingly, the unit may beinterposed substantially anywhere in the audio amplifier system as willbe readily understood. For example, in the above mentioned HammondPatent No. 2,230,836, such a system was interposed at about the centerof the audio channel circuitry whereas in Hannert Patent No. 2,967,447the signals applied thereto were taken from the voice coil terminationsand thereafter amplified after having been mechanically delayed.

In my unit, the electrical audio signals are applied by the usualshielded coaxial cable 10 through an opening inend wall 11 to theconventional flexible met-a1 terminals of a piezoelectric crystal 12.Crystal 12 is in itself rigid and is preferably of the type which reactsto electrical signals by twisting physically. Such crystals are mostcommonly used in phonographs where they translate twisting motionderived from the needle into electrical signals. Of course, they alsooperate in reverse, i.e., they produce a mechanical twisting motion inresponse to electrical signals applied thereto. Actually, forconvenience of mounting and protection of the terminals, I provide acovering of ordinary electrical friction tape 13 over the crystal andits flexible terminals as will be hereinafter described. For groundingpurposes, I ooat the inner surface of wall 11 with metal foil 14. Theshield of cable 10 is effectively grounded to foil 14 as is conventionaland as will be hereinafter more fully explained.

The spring delay system comprises the two coil springs 15 and 16 whichare hooked to each other and serially connected together as by solder attheir meeting point 17. The springs are of the type described in theabove mentioned patents, it being understood that the springs arelargely conventional and are not critical in either length, tension orcaliber. As an example, however, it may be noted that in a satisfactoryembodiment the smaller caliber spring 16 (about 1 diameter) was about 2inches long, the larger caliber spring (about V 3 diameter) being aboutthe same length. In such embodiment, the connected springs were extendedto about 6 inches, serially. The spring system is enclosed within annetal or other rigid tube 18 which is shock mounted at both ends infoam rubber or plastic blocks 19 which are adhered to a rigid supportingbase 20.

Notwithstanding the mounting of the unit in the highly resilient blocks19, the unit is nevertheless subject to external vibrations whichproduce spurious signals as above described. Accordingly, the connectionof the springs to the piezoelectric crystals is of great importance, asI have above set forth.

Referring now to larger spring 15, the end two coils thereof are bentperpendicularly to the axis of spring 15 so as to form a fasteningelement 21 comprised of said two end coils. Said fastening element 21 isthen glued to the friction tape 22 which embraces the crystal 23. A firmconnection is thus eifected which allows no play between the fastenerelement 21 and the rigid crystal 23. The glue may be of any commonvariety which will bond steel coils to the fabric friction tape 22.

The length of the crystal 23 is about as is the 'crystal 12. The otherend of crystal 23 is similarly adhesively secured to the fasteningspring coil 24 which in fact may constitute about 1 /2 turns. However, asingle annulus will suffice. Coil 24 is, of course, of metal as are thesprings 15 and 16. Fastening coils 21 and 24, although of spring metal,comprise horizontally rigid con- Patented June 4, 1963 necting elementscapable of transmitting physical movements without losses.

The enlargement of FIGURE 3 best illustrates the connection which formsthe subject of this invention. Thus end wall 25 duplicates the structureof the opposite end wall 11. It includes an inner foil 26 and is formedwith an offset hole within which is disposed a tubular rivet 27 servingas a passageway. The rivet further mechanically secures the fasteningmember 28 to wall 25.

The construction of fastening member 28 is of importance. It comprises aconnecting arm 29 and an end hook 30. End hook 30 has a planar floor3-1. Coil 24 although being connected firmly by adhesive 32 to thecrystal, or rather its tape cover 22, is pivotally received within hook30 so that it is free to swing upwardly in the direction of arrow 33 ordownwardly in the direction of arrow 34.

As a result of the foregoing connection, the springs may partake ofvarious motions relative to the tubular casing 18. Thus, the crystal 23,which is rigid with respect to the fastening end coils 21 of spring 15,may swing upwardly or downwardly in a vertical plane in the direction ofarrows 33 and 34 and it may also slide perpendicularly thereto in ahorizontal plane on floor 31, all without generating and transmittingelectrical signals to its flexible metallic terminals 35 and 36.Terminals 35 and 36 are the usual flexible Phosphor bronze (or the like)terminals connected to the crystal and which are in turn connected tothe wires 37 and 38 of the output coaxial cable 40, the shield 3-9 ofwhich is grounded to the arm 29 as illustrated in FIGURE 3.

It will be understood from the foregoing that when the receiving crystal23 receives a twisting impulse from the springs 15 and 16, it willproduce corresponding electrical signals in its terminals 35 and 36which are then amplified, although after some delay. However, should thesprings be jarred through external vibrations, the described structurewill effectively screen out such movements by the connection of the coil24 to the hook 30 which will produce a response only to twisting of thecrystal and not to movement thereof bodily. In other words, by virtue ofthe construction shown if fastening coil 21 is twisted, then coil 24will hold fast in hook 30 so as to produce twisting of the crystal andcorresponding electrical signals. However, should substantially anyother type of motion be applied to the receiving crystal 23, it willsimply move bodily and produce no signals.

The same fact applies to the input transducer or sending crystal 12, themounting thereof being identical to that of the output transducer 23,the fastening member 28 being spaced from its opposed fastening member41 by the length of tube 18.

Crystals 12 and 23 comprise flat bodies, the fastening coils 21 and 24being flatly adhered thereto by having an arc of about 120 thereofadhesively secured to the op posite end portions of the crystal bodieswhich are rectangular in shape.

Briefly, it may be observed that electrical audio signals translatedinto sound vibrations by crystal 12 will travel along the length ofsprings 16 and 15 and will be reflected from the ends thereof as well asfrom the connection point 17. The result will be a variety ofreflections substantially duplicating or at least simulating the soundreflections or reverberations in a large auditorium. However, outsideinfluences will be screened out as above described.

In the form shown, the output co-axial cable 40 is brought around to thefront of the unit for convenience in installation, both cablesterminating in plugs 42 and 43.

There has been shown what is now considered a preferred embodiment ofthe invention but it is obvious that changes and omissions may be madewithout departing from its spirit.

What is claimed is:

1. Apparatus for transmitting sound comprising opposed end supports, asending piezoelectric crystal and a receiving piezoelectric crystalrespectively connected to said supports, both of said crystals havingflat bodies, and an elongated spring means connected to and between saidflat bodies, the connection of said spring means to at least one of saidflat bodies comprising a portion of said spring means fixedly secured tothe said one flat body, said spring means consisting of at least onecoil spring, said last-named connection comprising an end coil thereofwhich is adhesively secured to said one flat body and embraces an endportion thereof, a hook having a substantially planar floor on each ofsaid end supports, and a rigid connecting element fixedly secured to theopposite end portion of said one flat body and being rotatably receivedby said hook and resting on and across said planar floor thereof wherebysaid rigid connecting element may rotate in the plane of said floor andin a plane perpendicular thereto but is restrained from twistingmovement relative to said hook.

2. Apparatus according to claim 1 and wherein said rigid connectingelement comprises an annular coil an arc of which is adhesively securedflatly to said flat body while an opposite arc thereof rests slidably onsaid hook floor.

3. Apparatus according to claim 2 and wherein the connection of each ofsaid flat bodies to said elongated spring means and to said hooks isidentical.

4. Apparatus for transmitting sound comprising a pair of opposedfastening members, means maintaining said fastening members in spacedrelationship, a piezoelectric crystal slidably connected to eachfastening member for slidable movement relative thereto in one plane androtating movement in a plane perpendicular to said one plane, saidcrystal being secured against twisting movement relative to saidfastening members, spring means disposed between and connected to saidcrystals for transmitting sound vibrations, one of said crystals being asending crystal and the other being a receiving crystal, the sendingcrystal reacting to sound signals by twisting and the receiving crystalreacting to twisting by generating electrical signals, each of saidfastening members comprising a hook having a planar floor, said crystalshaving flat bodies, a rigid connecting element connected flatly to theouter end portions of each crystal and being also slidably connected tosaid hook and resting on said planar floor thereof, said spring meanscomprising at least one coil spring and having an end coil thereoffixedly secured to an inner end portion of one of said crystals.

5. Apparatus according ,to claim 4 and wherein said rigid connectingelement comprises an annular coil an arc of which is adhesively securedflatly to the respective crystal bodies while an opposite arc of whichrests slidably on the respective hook floors.

6. Apparatus according to claim 5 and wherein said spring meanscomprises two serially connected coil springs of respectively differentcalibers.

References Cited in the file of this patent UNITED STATES PATENTS1,852,795 Wegel Apr. 5, 1932 2,001,132 Hansell May 14, 1935 2,137,852Nicolson Nov. 22, 1938 2,211,205 Hammond Aug. 13, 1940 2,318,417 PhelpsMay 4, 1943 2,575,333 Di Toro Nov. 20, 1951 2,600,870 Hathaway June 17,1952

1. APPARATUS FOR TRANSMITTING SOUND COMPRISING OPPOSED END SUPPORTS, ASENDING PIEZOELECTRIC CRYSTAL AND A RECEIVING PIEZOELECTRIC CRYSTALRESPECTIVELY CONNECTED TO SAID SUPPORTS, BOTH OF SAID CRYSTALS HAVINGFLAT BODIES, AND AN ELONGATED SPRING MEANS CONNECTED TO AND BETWEEN SAIDFLAT BODIES, THE CONNECTION OF SAID SPRING MEANS TO AT LEAST ONE OF SAIDFLAT BODIES COMPRISING A PORTION OF SAID SPRING MEANS FIXEDLY SECURED TOTHE SAID ONE FLAT BODY, SAID SPRING MEANS CONSISTING OF AT LEAST ONECOIL SPRING, SAID LAST-NAMED CONNECTION COMPRISING AN END COIL THEREOFWHICH IS ADHESIVELY SECURED TO SAID ONE FLAT BODY AND EMBRACES AN ENDPORTION THEREOF, A HOOK HAVING A SUBSTANTIALLY PLANAR FLOOR ON EACH OFSAID END SUPPORTS, AND A RIGID CONNECTING ELEMENT FIXEDLY SECURED TO THEOPPOSITE END PORTION OF SAID ONE FLAT BODY AND BEING ROTATABLY RECEIVEDBY SAID HOOK AND RESTING ON AND ACROSS SAID PLANAR FLOOR THEREOF WHEREBYSAID RIGID CONNECTING ELEMENT MAY ROTATE IN THE PLANE OF SAID FLOOR ANDIN A PLANE PERPENDICULAR THERETO BUT IS RESTRAINED FROM TWISTINGMOVEMENT RELATIVE TO SAID HOOK.